A high-grade oil has been produced from fractures in the Mancos shale section of the Rangely field for many years. A study of these fractures reveals that they belong to two distinct systems: a predominant system trending northeast-southwest part way across the field, and a subsidiary system situated south of and parallel with the axis of the fold. These fractures can be related to axial bending and arching in the Rangely anticline. Production in the Mancos shale section of this pool is entirely dependent on sustained openings in the fractures. The quantity of oil produced is small in comparison with that derived from the Weber sandstone of this field, but the Mancos pool has produced in excess of 4,500,000 barrels of oil.

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